1. Technical Field
The present invention relates to a portable and collapsible stair, and more particularly, to such a stair which particularly lends itself to a more convenient upward and downward walking motion.
2. Background Art
There are various occasions where a person must walk from one level to another while carrying various objects. A typical situation is where a boat is alongside a dock, and the upper edge of the side wall of the boat is positioned above the dock level. Quite often, a person boarding the boat will be carrying various supplies. Conventional stepladders are generally rather difficult to use in these situations, one of the reasons being that the lateral spacing of the support platforms or rungs is not great enough to permit a more normal upward walking motion.
A further consideration is that the ladder or stair must provide a broad and sturdy support structure when in its use position, and yet be able to be conveniently moved to its collapsed or stowage position, where the stepladder or stair is as compact as possible. Yet another consideration is the ladder or stair be structurally simple and constructed in the manner so that the manufacturing process can be accomplished economically.
A search of the patent literature has revealed a number of ladders, step stools, tables and the like. These are as follows.
U.S. Pat. No. 3,999,629--Schaffer et al illustrates a step stool where there are two main support members having vertical legs which cross one another. There is an upper support platform extending between upper ends of the legs, and a lower support platform extending between the legs below their pivot connecting location.
U.S. Pat. No. 3,166,028--Zagel shows a table which in general has the same overall configuration as the Schaffer et al patent discussed immediately above.
U.S. Pat. No. 3,058,544--Rossi et al shows a folding stool where there are two horizontal support platforms. One of the platforms is pivotally connected by its rear edge to the legs of one support member, and its forward end is supported from the upper ends of the legs of a second support member. There is a lower support platform having its rear edge portion connected to the legs of the second support member, and having its forward edge portion supported from the legs of the first support member.
U.S. Pat. No. 2,871,075--Stone shows a collapsible table having two inverted U-shaped support members. In the operating support position, upper cross members of the two support members support the platform which is the table.
U.S. Pat. No. 2,643,925--Derman shows a collapsible service table somewhat similar to that shown in the Stone patent discussed immediately above.
U.S. Pat. No. 2,217,658--De Puy shows a folding bath stand and dressing table for an infant. There are two support members, each having downwardly extending legs. There is an upper dressing table 9 positioned between the upper ends of the legs, and there is a lower support platform supported from one pair of legs, and positioned substantially directly below the upper dressing table.
U.S. Pat. No. 1,406,888--Pandolfo shows a collapsible chair having two pairs or crossed legs, with the seat of the chair extending between upper edges of the legs.
U.S. Pat. No. 1,222,673--Rizzo shows what is called a "convertible chair". When functioning as a chair, there are two first support legs which extend upwardly and rearwardly and two second support legs which extend upwardly and forwardly, with the two pair of legs being pivotally connected at intermediate locations. The chair platform has its rear edge pivotally connected to the first set of legs below the pivot connection and extends forwardly therefrom. There is a support member pivotally connected to a lower end portion of the first legs and extending upwardly and forwardly to support the chair platform. There is an upper movable panel 28 that is gripped between two laterally spaced blocks 27. In the chair configuration and in the stowed configuration, this panel 28 extends upwardly from the upper end portions of the first legs. In FIG. 7, the convertible chair is shown in a stepladder configuration where the panel 28 is supported from the upper ends of the two pairs of legs.
U.S. Pat. No. 362,379--Henry shows a folding stool where there is a support platform supported from the upper ends of two pairs of crossed legs.